A known apparatus for determining the potential alpha energy of radon daughters in the air is disclosed in Frank, A. L., E. V. Benton.-Nucl. Track Detection, 1, 149 (1977). This known apparatus comprises a fixed aerosol filter on which, because of the continuous aspiration of air, there are deposited aerosols containing radon and thoron daughters. The radiations of the radon and thoron daughters are recorded by two solid-state trace detectors. Between the detectors and the filters there are disposed absorbers of different thickness, which reduce the energy of the alpha particles to limits suitable for measurement. On the basis of the indications of both detectors, the potential alpha energy of the radon daughters are determined by means of formulas.
The disadvantages of this known apparatus lie in its low productivity. The filter must be replaced frequently and the volume specific activities of the radon daughters and the volume specific activites and the potential alpha energy of the thoron daughters are not determined separately.
Another known apparatus for measuring the potential alpha energy of radon daughters an the air is disclosed in Solomon, S. R.. et al.-Health Phys., v.52, 143 (1987). This known apparatus comprises an aerosol filter, clamped between two rings, in each of which there is mounted a thermoluminescent detector in the form of a disk with a round hole in the center. This configuration is mounted in a cylindrical housing (head) consisting of two parts, interconnected by means of a fastening thread. The one end of the housing is connected to an air pump, while the other is provided with a hole for sucking in air. On the basis of the indications of the detectors, the potential alpha energy of the radon daughters is determined by means of formulas or graphs. The share of the thoron daughters is determined as follows: after the measuring of the potential alpha energy of the radon daughters, the aerosol filter is removed, a new head with new thermoluminescent detectors is mounted and, on the basis of their indication after 24 hours, the share of the indications of the thermoluminescent detectors due to the thoron daughters is determined.
The drawbacks of this known apparatus lie in its limited functional possibilities. The volume specific activities of the radon and the volume specific activities and the potential alpha energy of the thoron daughters in the air are not determined separately. The filter requires frequent replacement and additional operations are required for taking into account the influence of the thoron daughters. Moreover, this apparatus exhibits low accuracy due to systematic error as a result of the dependence of the detector indications on the differences in the relations of the volume specific activities of the radon daughters (at constant potential alpha energy).
It is therefore a general object of this invention to develop an apparatus for measuring the time-integrated volume specific activities and the potential alpha energy of radon and thoron daughters in the air, which has wide functional possibilities, high productivity and high accuracy.